Self-consistent theory of a homogeneous binary Bose mixture with strong repulsive interspecies interaction

TL;DR

This paper develops a mean-field theory for a two-component Bose mixture with strong repulsive interspecies interactions, revealing conditions under which the mixture remains stable and miscible beyond traditional weak-interaction criteria.

Contribution

It introduces an analytical mean-field approach that extends the understanding of phase boundaries in strongly interacting binary Bose gases, surpassing previous weak-interaction models.

Findings

System can remain stable and miscible for larger interspecies interactions at finite temperature.

Derived analytical expressions for phase boundary and miscibility criteria.

Shows stability depends on gas parameter and temperature, not just interaction strength.

Abstract

Multicomponent quantum gases are ideal platforms to study fundamental phenomena arising from the mutual interaction between different constituents. Particularly, due to the repulsive interactions between two species, the system may exhibit a phase separation. We develop a mean-field-based theory for a two-component Bose mixture, which is equivalent to the Hartree-Fock-Bogoliubov approximation, and derive analytical expressions for the phase boundary and miscibility. The majority of existing theories, which are valid only for weakly interacting Bose gases, predict that the phase boundary is determined by the criterion $g_{ab}\leqslant\sqrt{g_{aa} g_{bb}}$ (where $g_{ab}$ is a coupling constant between the components $a$ and $b$). We show that in the Bose-Einstein-condensation phase ($T\leqslant T_c$) the system may remain in a stable and miscible phase also for larger values of $g_{ab}$, depending on the gas parameter $\gamma$ and temperature.